Project Summary The long-term goal of this project is to develop a wireless, wearable system to estimate the tension in tendons of the legs during dynamic movements. Tendon tension provides an estimate of muscle force, which is important information for understanding biomechanical behavior in all types of movement, though it has previously been difficult to measure. Recent advances have shown that skin-mounted accelerometers can track the propagation of shear waves along a tendon, after the waves are induced by a light mechanical tap on the tendon. The speed of wave propagation depends on the tension in the tendon, so measuring wave speed provides a measurement of tendon tension. The proposed project will build and test a wearable system to make these tendon tension measurements during free movement. These measurements promise to enable new methods of injury assessment, rehabilitation, athletic training, and treatment of musculoskeletal disorders. This research will investigate the ability of a mobile system to make measurements that match the quality of laboratory systems, and the ability of tendon tension measurements to provide insight into biomechanics during movement in everyday environments. The Specific Aims of this project are to: 1. To design, build, and validate a wearable system for measuring tendon tension through measurements of shear wave propagation speed in tendon. 2. To investigate the utility of wearable tendon tension measurements for assessing biomechanical function during real-world activities.